William Spengler, 62, opened fire on the volunteers as they responded to a blaze in Webster just before 6 a.m. ET Monday in a small cluster of homes near Lake Ontario, police said.

Michael Chiapperini, 43, a lieutenant with the Webster police, and Tomasz Kaczowka, 19, were shot dead, and Spengler killed himself as seven houses burned around him.

"We are being shot at," an unidentified voice told a 911 dispatcher in a recording aired Wednesday on NBC's TODAY. "Multiple firemen down. Multiple firemen are shot. I am shot. I think he is using an assault rifle."

Police investigating Monday’s killings said Tuesday that they had found what appeared to be human remains at the gunman's home. Authorities said they believed the remains were those of Spengler’s 67-year-old sister, Cheryl, who lived with him.

Two other firefighters, Joseph Hofstetter and Theodore Scardino, were shot but survived. One was struck by a bullet in the pelvis and the other in the chest and knee, NBCNewYork.com reported. It said the two were described as stable in a hospital and were expected to survive.

Cops said Spengler left a three-page typewritten note saying he wanted to burn down the neighborhood and "do what I like doing best, killing people."

The Rochester Democrat and Chronicle said Wednesday that the funeral for Chiapperini, who was also a 20-year veteran of the Webster Police Department, will be Sunday, while a funeral Mass for Kaczowka, who graduated from high school last year, will be celebrated in Rochester at 10 a.m. ET Monday.

Spengler had lived in the house with his sister and mother, Arline, who died in October at 91. Arline Spengler's obituary asked that memorial donations be made to the West Webster Fireman's Association.

A former neighbor told The Associated Press that Spengler "loved his mama to death" and that he "couldn't stand" his sister. The neighbor said he thought Spengler "went crazy" after his mother died.

Spengler was convicted of manslaughter in 1981 after the death of his grandmother, Rose Spengler, 92, and was paroled in 1998. He remained under parole supervision until 2006, the Democrat and Chronicle reported. Before Monday's shooting, Webster police hadn't had any run-ins with Spengler since he was paroled, they said.

Although Spengler couldn't legally own firearms as a convicted felon, police said he was armed with a Smith & Wesson .38 revolver, a 12-gauge pump shotgun and a Bushmaster .223 caliber rifle.

At least 33 people were displaced by the fire, which engulfed at least seven homes and a motor vehicle.

Ron Mott, Jason White and Andrew Mach of NBC News, NBCNewYork.com and The Associated Press contributed to this report.